One day, Miho, the older sister of Amu's husband, turns up at her house. In fact, she is a lesbian who ran away from home after a fight with her cohabiting girlfriend. She has been in a rut with her husband and has not had sex for a year, so perhaps she has a gap in Kokoro. Amu is gradually Kokoro by Miho, who exudes a unique sexiness. Eventually, the two of them cross the line and enter into a forbidden relationship...